According to the International Centre for Prison Studies, the United States has the highest prison population per capita in the world. In 2009, for example, 1 out of every 135 U.S. residents was incarcerated. Generally, inmates convicted of felony offenses serve long sentences in prison (e.g., federal or state prisons), whereas those convicted of misdemeanors receive shorter sentences to be served in jail (e.g., county jail). In either case, while awaiting trial, a suspect or accused may remain incarcerated. During his or her incarceration, an inmate may have opportunities to communicate with the outside world.
The scope of what constitutes communication to the inmate population has traditionally consisted of voice-only telephone systems. In that context, a Communication Detail Record (CDR), also known as Communication Data Record, is a record produced by a telecommunications device that contains attributes that are specific to a phone call handled by that device.
Generally speaking, a CDR may contain metadata having data fields that describe a specific instance of a telecommunication transaction, but does not include the contents of that transaction—e.g., it does not include audio data or recordings. By way of an example, a CDR describing a particular phone call may include attribute such as: the phone number of the subscriber originating the call (calling party), the phone number receiving the call (called party), the starting time of the call (date and time), the call duration, the billing phone number that is charged for the call, the identification of the telephone exchange or equipment writing the record, a unique sequence number identifying the record, additional digits on the called number used to route or charge the call, the disposition or the results of the call (indicating, for example, whether or not the call was connected), the route by which the call entered the telephone exchange, the route by which the call left the exchange, etc.